This invention relates cleaning of stack gases such as those from coal fired power plants, from natural or propane burning heating plants, or from cement kilns. The stack gases exhausted from each such facility is controlled by environmental regulations. Such regulations require abatement of carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxide (NOx), sulfur oxide (SOx); as well as abatement of halogens, such as chloride and fluorides, and trace metals, particularly mercury, lead, and zinc.
Various methods and apparatus have been proposed for abating these pollutants in stack gases. In particular, a variety of methods have been proposed for reducing pollutants released from coal-fired stack gas. One method for cleaning coal-fired stack gas is the use of scrubbers that inject a liquid or slurry into a gas stream that washes various pollutants, such as acidic compounds, from the exhaust stream. Another method for cleaning coal-fired stack gas is the use of an exhaust burner that combusts volatile materials and other compounds reducing pollution in the stack gas.
Specifically, it has been proposed that the stack gases be mixed with ammonia or urea and then passed through a catalyst in which the ammonia reacts selectively with the nitrous oxides to form nitrogen gas in water vapor, or combustion of a sulfur-containing fossil fuel in the presence of a calcium carbonate or magnesium carbonate to form calcium sulfate or magnesium sulfate. See U.S. Pat. Nos. 8,181,451; 6,706,246; 5,525,317; 5,237,939; 4,185,080; and 4,051,225. It has also been proposed reducing nitrogen in stack gas by passing the stack gas through a heat exchange having a SCR catalyst. See U.S. Pat. No. 5,918,555. Likewise, it has been proposed reducing sulfur oxide content in stack gases by catalyzed oxidation to sulfur trioxide in the presence of an absorbent or combusting sulfur-containing fuel in a combustion zone charged with a slurry in sulfuric acid solution. See U.S. Pat. Nos. 5,540,755; 4,649,034; 4,284,015; and 4,185,080.
It has also been proposed catalytically converting unburned hydrocarbons and carbon monoxide to carbon dioxide and reducing nitrogen oxides to nitrogen subsequent to the combustion of fossil fuels while absorbing sulfur oxide, where the catalytic material is physically combined onto a dry powder of an adsorbent matrix select from calcium aluminate, calcium aluminate cement, barium titanate, and calcium titanate. See U.S. Pat. No. 4,483,259. Similarly, it has been proposed to pass the stack gases through a catalyst bed of a combination of active metals on the surface that is capable of reducing or converting sulfur oxides, carbon monoxide and hydra carbons to inert compounds such as carbon dioxide, water and nitrogen. See U.S. Pat. No. 7,399,458. Levels of mercury in stack gases from coal combustion have also been reduced by introducing a sorbent composition into the gas stream in a zone where temperature is greater than 500° C. and where the sorbent composition comprises an effective amount of nitrate salt and/or a nitrite salt. See U.S. Pat. Nos. 7,468,170 and 7,731,781.
However, these previous proposals have a number of drawbacks. Many require addition of another gas such as ammonia sulfuric acid, or the presence of an active metal catalyst. One particular problem unresolved by current technology is carbon gaseous pollutants that cannot be reduced by scrubbing, combustion, or capture. It has been proposed to capture the carbon in the form of carbon dioxide, compress the carbon dioxide, and storing it in a geological formation. Zeolite has been proposed among others as a material to absorb carbon dioxide, and after sequestering the carbon dioxide then to be able to regenerate the zeolite material. See “Carbon Dioxide Capture Using a Zeolite Molecular Sieve Sampling System for Isotopic Studies (13C and 14C) of Respiration”, Radiocarbon, 47, 441-451 (2005); “Absorbent Materials for Carbon Dioxide Capture from Large Anthropogenic Point Sources”, ChemSusChem 2009, 2, 796-854; “NIST Provides Octagonal Window of Opportunity for Carbon Capture”, NIST Techbeat, Feb. 7, 2012. However, these uses of zeolite involved large particle sizes of zeolite; for example, between 1/16 and ⅛ inch in size under conditions to provide for adsorption of carbon dioxide and later regeneration. These methods of absorbing carbon dioxide highlight the continuing problem of disposing of the sequestered carbon dioxide.
There is therefore still a need for a method and apparatus to effectively remove carbon monoxide, carbon dioxide, nitrous oxides, sulfur oxides and trace metals, such as mercury, from stack gases without consuming expensive catalysts, without injecting additional gases and solids into the stack gas, and without creating waste products that, themselves, present problems in disposal. This is of particular concern in cleaning of coal-fired stack gas from fire power plants because of the release of volatiles such as coal tar and other active pollutants along with carbon dioxide in the stack gas.
Presently disclosed is a method of cleaning stack gases comprising the steps of:                (a) providing in a stack adapted to pass stack gases through a first catalytic flow-through bed of calcium zeolite comprising natural zeolite particles of a majority between 44 μm and 64 μm in size at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce carbon oxides in the stack gases;        (b) providing in the stack adapted to pass stack gases positioned adjacent the first catalytic flow-through bed, a second catalytic flow-through bed of a blend between 25 and 75% of sodium zeolite and calcium zeolite comprising natural sodium and calcium zeolite particles of a majority between 65 μm and 125 μm in size at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce nitrogen oxides in the stack gases;        (c) providing in the stack adapted to pass stack gases positioned adjacent the second catalytic flow-through bed, a third catalytic flow-through bed of calcium zeolite comprising natural zeolite particles of a majority between 78 m and 204 m at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce sulfur oxides in the stack gases; and        (d) passing stack gases selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln sequential through the first catalytic bed, the second catalytic bed, and the third catalytic bed each collecting materials in the catalytic beds and providing gas exiting the third catalytic bed with at least 70% reduction in sulfur oxides, nitrogen oxides and carbon oxide.        
The method where the stack gas is sequentially circulated through the first catalytic bed, the second catalytic bed, and the third catalytic bed may also involve removal from the stack gas of at least 50% or 70% of mercury in all forms.
Also disclosed is a method of cleaning stack gases comprising the steps of:                (a) providing in a stack adapted to pass stack gases through a first catalytic flow-through bed of calcium zeolite comprising natural zeolite particles of a majority between 44 μm and 64 μm in size at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce carbon oxides in the stack gases;        (b) providing in the stack adapted to pass stack gases positioned adjacent the first catalytic flow-through bed, a second catalytic flow-through bed of a blend between 25 and 75% of sodium zeolite and calcium zeolite comprising natural sodium and calcium zeolite particles of a majority between 65 μm and 125 μm in size at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce nitrogen oxides in the stack gases;        (c) providing in the stack adapted to pass stack gases positioned adjacent the second catalytic flow-through bed, a third catalytic flow-through bed of calcium zeolite comprising natural zeolite particles of a majority between 78 μm and 204 μm at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce sulfur oxides in the stack gases;        (d) passing stack gases selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln sequential through the first catalytic bed, the second catalytic bed, and the third catalytic bed each collecting materials in the catalytic beds and providing gas exiting the third catalytic bed with at least 70% reduction in sulfur oxides, nitrogen oxides and carbon oxide; and        (e) purging solids and liquids from the first catalytic bed, the second catalytic bed, and the third catalytic bed by intermittently passing nitrogen through the beds to remove solids and liquids collected from the stack gases by the beds.        
Again, the method where the stack gas is sequentially circulated through the first catalytic bed, the second catalytic bed, and the third catalytic bed may also involve removal from the stack gas of at least 50% or 70% of mercury in all forms.
In any case, the method may also comprise in addition a fourth catalytic flow-through bed of calcium zeolite comprising natural zeolite particles between 44 μm and 64 μm in size positioned in the stack before the first catalytic bed with an electrical charge on said fourth catalytic flow-through bed. The fourth catalytic flow-through bed serves to separately collect bauxite compounds from the stack gases before passing through the first catalytic bed.
In any event, the method may also involve the gases exiting a stack from the third catalytic bed, whether or not a fourth catalytic flow-through bed is used, with at least 90% or 95% reduction in bauxite compounds, sulfur oxides, nitrogen oxides, mercury oxide, and carbon oxide compared to the stack gases delivered through the stack.
In any event, the method may involve where the stack gas is circulated through the first catalytic bed, the second catalytic bed, and the third catalytic bed, each positioned between screens of between 150 and 250 mesh. In addition or alternatively, the first catalytic bed, the second catalytic bed, and the third catalytic bed may each be provided on a moving disk. The method may alternatively involve at least two series of sequential circulations through the first catalytic bed, the second catalytic bed, and the third catalytic bed provided in parallel so that the stack gases can be cleaned by the method through one series of beds while other series of the beds can be cleaned as described below.
The method may alternatively be practiced separately to reduce carbon monoxide and dioxide, sulfur oxides and/or nitrogen dioxides. This is particularly the case with stack gas from cement kilns and other plants, which tend to focus on carbon dioxide.
Also disclosed is an alternative method of cleaning stack gases comprising the steps of:                (a) providing in a stack adapted to pass stack gases of less than 7% oxygen through a first catalytic flow-through bed of calcium zeolite comprising natural zeolite particles at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce carbon oxides from the stack gases and increase oxygen levels in the stack gas;        (b) providing in the stack adapted to pass stack gases positioned adjacent the first catalytic flow-through bed, a second catalytic flow-through bed of a blend between 25 and 75% of sodium zeolite and calcium zeolite comprising natural sodium and calcium zeolite particles at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce nitrogen oxides from the stack gases and increase oxygen levels in the stack gas;        (c) providing in the stack adapted to pass stack gases positioned adjacent the second catalytic flow-through bed, a third catalytic flow-through bed of calcium zeolite comprising natural zeolite particles at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce sulfur oxides in the stack gases and increase oxygen levels in the stack gas; and        (d) passing stack gases of less than 7% oxygen selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln sequential through the first catalytic bed, the second catalytic bed, and the third catalytic bed each collecting materials catalytic beds and providing gas exiting the third catalytic bed with at least 70% reduction in sulfur oxides, nitrogen oxides and carbon oxide and greater than 15% oxygen.        
In this alternative method, the beds providing the first catalytic bed, the second catalytic bed, and the third catalytic bed may also involve the removal from the stack gas of at least 50% or 70% of mercury. The oxygen exiting the third catalytic bed may be recirculated through the burners to provide fuel for the combustible system.
In any case, the alternative method may also comprise in addition a fourth catalytic flow-through bed of calcium zeolite comprising natural zeolite particles between 44 μm and 64 μm in size positioned in the stack before the first catalytic bed with an electrical charge on said fourth catalytic flow-through bed to collect bauxite compounds from the stack gases before passing through the first catalytic bed.
In any event, the alternative method may also involve the gases exiting a stack from the third catalytic bed, whether or not a fourth catalytic flow is used, providing at least 90% or 95% reduction in bauxite compounds, sulfur oxides, nitrogen oxides, mercury oxide, and carbon oxides compared to the stack gases delivered through the stack.
In any event, the alternative method may involve where the stack gas is circulated through the first catalytic bed, the second catalytic bed, and the third catalytic bed, each positioned between screens of between 150 and 250 mesh. In addition or alternatively, the first catalytic bed, the second catalytic bed, and the third catalytic bed may each be provided on a moving disk. The method may alternatively involve at least two series of sequential circulations through the first catalytic bed, the second catalytic bed, and the third catalytic bed provided in parallel so stack gas can be cleaned by the method through one series of beds while other series of the beds can be purged as described below.
The alternative method may be practiced separately to reduce carbon monoxide and dioxide, sulfur oxides and/or nitrogen dioxides.
Also disclosed is an apparatus for cleaning stack gases comprising:                (a) a first catalytic flow-through bed of natural calcium zeolite with a porosity of a total surface area of not greater than 1200 m2/g adapted to reduce sulfur oxides positioned in an exhaust stack;        (b) a second catalytic flow-through bed of a blend of natural sodium zeolite and natural calcium zeolite of a porosity with a total surface area of not greater than 1200 m2/g adapted to reduce nitrogen oxides positioned in the exhaust stack above the first bed;        (c) a third catalytic flow-through bed of natural calcium zeolite with a porosity of a total surface area not greater than 1200 m2/g adapted to reduce carbon oxides and mercury oxides positioned in the exhaust stack above the second bed; and        (d) the exhaust stack adapted to provide a gas flow selected from the group consisting of volatiles from combustion of coal or combustion of natural gas sequential through the first catalytic bed, the second catalytic bed, and the third catalytic bed each collecting solids in the catalytic beds and providing gas exiting the third catalytic bed with at least 70 or 90% reduction in sulfur oxides, nitrogen oxides, and carbon oxide.        
In the apparatus, the blend of natural sodium zeolite and natural calcium zeolite in the second catalytic bed may be between 25 and 75%. The apparatus having the first catalytic bed, the second catalytic bed, and the third catalytic bed may have provided between each bed on moving disks. Further, the first catalytic bed, the second catalytic bed, and the third catalytic bed may also have moving disks such that the stack gases in element (d) can be continually passed through the first catalytic bed, the second catalytic bed, and the third catalytic bed to provide collection of solids and/or liquids while other portions or beds of like compositions are purged with nitrogen to collect the solids and/or liquids from the beds. The apparatus may also be provided in the addition or in the alternative with first catalytic bed, second catalytic bed, and third catalytic bed adapted to be purged with gas or liquid nitrogen to collect the solids and/or liquids from the beds.
The apparatus may also be provided with a fourth catalytic flow-through bed positioned in the exhaust gases before the first catalytic bed with a porosity of a total surface area not greater than 1200 m2/g adapted to collect bauxite compounds before passage through the first catalytic bed. Alternatively, the first catalytic bed, the second catalytic bed, and the third catalytic bed each have a porosity of a total surface area not greater than 800 m2/g and the fourth catalytic flow, if used, may have a porosity of a total surface area not greater than 800 m2/g.
In any event, the apparatus may also provide the gases exiting a stack from the third catalytic bed, whether or not a fourth catalytic flow is used, with at least 90% or 95% reduction in bauxite compounds, sulfur oxides, nitrogen oxides, mercury oxide, and carbon oxides compared to the stack gases delivered through the stack. In the case of cement kilns, the focus is on the reduction of carbon dioxide.
Also disclosed is an apparatus for cleaning stack gases comprising:                (a) a first catalytic flow-through bed of natural calcium zeolite with a porosity of a total surface area of not greater than 1200 m2/g adapted to reduce sulfur oxides positioned in an exhaust stack;        (b) a second catalytic flow-through bed of a blend of natural sodium zeolite and natural calcium zeolite of a porosity with a total surface area of not greater than 1200 m2/g adapted to reduce nitrogen oxides positioned in the exhaust stack above the first bed;        (c) a third catalytic flow-through bed of natural calcium zeolite with a porosity of a total surface area not greater than 1200 m2/g adapted to reduce carbon oxides and mercury oxides positioned in the exhaust stack above the second bed;        (d) the exhaust stack adapted to provide a gas flow selected from the group consisting of volatiles from combustion of coal or combustion of natural gas or from a cement kiln sequential through the first catalytic flow-through bed, the second catalytic flow-through bed, and the third catalytic flow-through bed each catalytic bed collecting solids and providing stack gases exiting the third catalytic flow-through bed with at least 70% reduction in sulfur oxides, nitrogen oxides, and carbon oxide; and        (e) the first catalytic flow-through bed, the second catalytic flow-through bed, and the third catalytic flow-through bed are each provided on rotating disks such that the stack gases can be continually passed through the first catalytic flow-through bed, the second catalytic flow-through bed, and the third catalytic flow-through bed to provide collection of solids and/or liquids while other portions or beds of like compositions are purged with nitrogen to collect the solids and/or liquids from the beds.        
In the apparatus, the first catalytic flow-through bed, the second catalytic flow-through bed, and the third catalytic flow-through bed may each be positioned between screens each of between 150 and 250 mesh. The first catalytic flow-through bed, the second catalytic flow-through bed, and the third catalytic flow-through bed may each have a porosity of a total surface area not greater than 800 m2/g. The blend of natural sodium zeolite and natural calcium zeolite in the second catalytic flow-through bed may be between 25% and 75%.
In the apparatus, the exhaust stack may be adapted to exit gases from the third catalytic flow-through bed having at least 90% reduction in sulfur oxides, nitrogen oxides, and carbon oxide compared to the stack gases delivered to the first catalytic flow-through bed. Alternatively, the exhaust stack may be adapted to exit gases from the third catalytic flow-through bed having at least 95% reduction in sulfur oxides, nitrogen oxides, mercury oxide and carbon oxide compared to the stack gases delivered to the first catalytic flow-through bed.
The apparatus may further comprise at least two series of sequential first catalytic flow-through bed, second catalytic flow-through bed, and third catalytic flow-through bed provided in parallel so stack gases can be cleaned through one of the series of beds while other series of beds can be cleaned.
The apparatus may also further comprise a fourth catalytic flow-through bed of calcium zeolite provided in the exhaust stack below the first catalytic flow-through bed with a porosity of a total surface area not greater than 1200 m2/g adapted to collect bauxite compounds before passage through the first catalytic flow-through bed. The fourth catalytic flow-through bed may be provided in a rotating disk so the stack gases are continuously move there through while another portion of the disk is being purged with nitrogen. The fourth catalytic flow-through bed may have a porosity of a total surface area not greater than 800 m2/g.
In the apparatus, the exhaust stack may be adapted to exit gases from the third catalytic flow-through bed with at least 95% reduction in bauxite compounds, sulfur oxides, nitrogen oxides, mercury oxides, and carbon oxide compared to the stack gases delivered to the fourth catalytic flow-through bed.
Also disclosed herein is a fertilizer product produced by the steps of:                (a) providing in a stack adapted to pass stack gases through a first catalytic flow-through bed of calcium zeolite comprising natural zeolite particles of a majority between 44 μm and 64 μm in size at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce carbon oxides in the stack gases;        (b) providing in the stack adapted to pass stack gases positioned adjacent the first catalytic flow-through bed, a second catalytic flow-through bed of a blend between 25 and 75% of sodium zeolite and calcium zeolite comprising natural sodium and calcium zeolite particles of a majority between 65 μm and 125 μm in size at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce nitrogen oxides in the stack gases;        (c) providing in the stack adapted to pass stack gases positioned adjacent the second catalytic flow-through bed, a third catalytic flow-through bed of calcium zeolite comprising natural zeolite particles of a majority between 78 μm and 204 μm at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce sulfur oxides in the stack gases;        (d) passing stack gases selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln sequential through the first catalytic bed, the second catalytic bed, and the third catalytic bed each collecting materials in the catalytic beds and providing gas exiting the third catalytic bed with at least 70% reduction in sulfur oxides, nitrogen oxides and carbon oxide; and        (e) purging solids and liquids from the first catalytic bed, the second catalytic bed, and the third catalytic bed by intermittently passing nitrogen through the beds to remove solids and liquids collected from the stack gases by the beds.        
Alternatively disclosed herein is a fertilizer product produced by the steps of:                (a) providing in a stack adapted to pass stack gases of less than 7% oxygen through a first catalytic flow-through bed of calcium zeolite comprising natural zeolite particles at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce carbon oxides from the stack gases and increase oxygen levels in the stack gas;        (b) providing in the stack adapted to pass stack gases positioned adjacent the first catalytic flow-through bed, a second catalytic flow-through bed of a blend between 25 and 75% of sodium zeolite and calcium zeolite comprising natural sodium and calcium zeolite particles of at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce nitrogen oxides from the stack gases and increase oxygen levels in the stack gas;        (c) providing in the stack adapted to pass stack gases positioned adjacent the second catalytic flow-through bed, a third catalytic flow-through bed of calcium zeolite comprising natural zeolite particles at a temperature above the dew point between 125 and 500° F. and a pressure between 3 and 200 psi adapted to reduce sulfur oxides in the stack gases and increase oxygen levels in the stack gas; and        (d) passing stack gases of less than 7% oxygen selected from the group consisting of volatiles from combustion of coal or from combustion of natural gas or from a cement kiln sequential through the first catalytic bed, the second catalytic bed, and the third catalytic bed each collecting materials in the catalytic beds and providing gas exiting the third catalytic bed with at least 70% reduction in sulfur oxides, nitrogen oxides and carbon oxide and greater than 15% oxygen.        
Also disclosed herein is a fertilizer product produced by the steps of:                (a) providing a first catalytic flow-through bed of natural calcium zeolite with a porosity of a total surface area of not greater than 1200 m2/g adapted to reduce sulfur oxides in a stack gas;        (b) providing a second catalytic flow-through bed of a blend of natural sodium zeolite and natural calcium zeolite with a porosity of a total surface area of not greater than 1200 m2/g adapted to reduce nitrogen oxides in a stack gas with the blend of sodium zeolite and calcium zeolite between 25 and 75%;        (c) providing a third catalytic flow-through bed of natural calcium zeolite with a porosity of a total surface area not greater than 1200 m2/g adapted to reduce carbon oxides and mercury oxides in a stack gas;        (d) passing stack gases selected from the group consisting of volatiles from combustion of coal or combustion of natural gas sequential through the first catalytic bed, the second catalytic bed, and the third catalytic bed each collecting solids and liquids in the catalytic beds and providing gas exiting the third catalytic bed with at least 70% reduction in sulfur oxides, nitrogen oxides, and carbon oxide; and        (e) purging the solids and liquids collected on the from the first catalytic bed, the second catalytic bed, and the third catalytic bed and collecting said solids and liquids purged from the first catalytic bed, the second catalytic bed, and the third catalytic bed to provide a fertilizer product.        
In any case, the fertilizer product may be purged with gas or liquid nitrogen. The fertilizer product may be produced where the beds providing the first catalytic bed, the second catalytic bed, and the third catalytic bed are each positioned between screens of between 150 and 250 mesh. Alternatively, the fertilizer product may be produced with the stack gas pasted through a fourth catalytic flow-through bed before passage through the first catalytic bed with a porosity of a total surface area not greater than 1200 m2/g adapted to collect bauxite compounds before passage through the first catalytic bed.
In the fertilizer product, the gases exiting a stack from third catalytic bed may be at least 90% or 95% reduction in sulfur oxides, nitrogen oxides, mercury oxide and carbon oxide from the stack gases delivered to the a first catalytic flow-through bed. In the alternative, the gases exiting the third catalytic bed may be at least 90% or even 95% reduction in bauxite compounds, sulfur oxides, nitrogen oxides, mercury oxide, and carbon oxide from the stack gases where the stack gas is delivered to the beds through a fourth catalytic flow.
In the various embodiments of the method, apparatus or fertilizer product, the stack gas may include carbon monoxide (CO), carbon dioxide (CO2), nitrous oxide (NOx), sulfur dioxide (SO2) and nitrous dioxide (NO2). The solid waste may also include nitrate salt formed by reaction of nitrogen and nitrogen compounds retained in the zeolite beds with available oxygen. And exit from the third catalytic bed will typically include excess oxygen from the reduction according in the first, second and third catalytic beds, as described above. The apparatus may also include product purged with liquid nitrogen.
In any case, the exiting stack gas with increased oxygen levels may be returned from the gas cleaning system to the burner where it is combusted with the coal or natural gas. The system may also include a solid waste draw for collecting the materials and drawing them away from the gas cleaning section.
Other details, objects and advantages of the present invention will become apparent from the description of the preferred embodiments described below in reference to the accompanying drawings.